This invention relates to heat exchangers and methods of making the same, and more particularly to heat exchangers of the type embodying outwardly projecting fins and methods of making same.
Heat exchangers having heat transfer elements embodying fins formed from the outer surface material of tubular members are known in the art and have been disclosed example in U.S. Pat. No. 3,202,212 to Richard W. for Kritzer, U.S. Pat. No. 3,692,105 to Joseph M. O'Connor, and U.S. Pat. No. 4,554,970 to Stephen F. Pasternak and Franz X. Wohrstein. These prior art heat transfer elements are formed from a length of tubular stock, preferably one having a rectangular transverse cross-section and with one or more openings extending longitudinally of the element to carry a heat exchanger medium, such as water, or other coolants. The fins are formed in a skiving operation in which a cutting tool is passed longitudinally along the upper and lower surfaces of the tubular element, cutting or gouging the fins from longitudinally extending ribs provided on the surfaces of the tubular member.
In the Kritzer patent, the fins are in the form of spines formed from outwardly projecting ribs on the tubular member. In the O'Connor patent, fins are formed by cutting or gouging them from upwardly projecting ribs and the portion of the tubular member directly underlying the ribs, to thereby afford fins having elongated base portions projecting outwardly from the side wall of the tubular member, with spaced fins projecting outwardly from the outer longitudinal edges of the base portions. In the Pasternak et al patent, fins are cut or gouged from ribs on the sidewalls of the heat exchanger tubing by advancing a cutter into the ribs on the tubing. The position of the cutter is controlled to sever predetermined fins to provide predetermined fin-free areas on the sidewalls. This is accomplished by raising the cutter somewhat (in the order of three thousandths of an inch) toward the end of its forward stroke, defining fin severing stroked for forming the fin-free areas.
With present technology, the residual wall thickness for the tubing for these prior art units had to be in the order of 0.030 inches to 0.035 inches to provide the necessary strength in the heat exchanger tubing at return bend portions when the tube is bent into a serpentine pattern. Such wall thickness for the heat exchanger tubing was also required in the return bend portions for the heat exchanger tubing to withstand the considerable pressure forces present within the tube, particularly at the return bend portions which define the weak points of the heat exchanger assembly when it is in use. For these reasons, in heat exchanger units heretofore constructed, the dimensions of the tubing at the return bend portions dictated the dimensions of the heat exchanger tubing over its entire length.
Economic pressures exist to reduce the overall size and weight of heat exchanger units as well as the cost of such units. Thus, it would be desirable to have a heat exchanger unit of the fin type which is characterized by reduced overall weight as compared to a comparable size prior art heat exchanger unit and which requires less material for the heat exchanger tubing without compromising the strength of the heat exchanger tubing, particularly at the return bend portions thereof.